The present invention involves fibrous nonwoven mats having at least two layers with a surface layer having fine fibers and/or particles therein, both layers being well bonded together and to each other with a same resin binder. The mats produced according to this invention are useful as a facer for all types of boards such as wood boards, wood product boards, insulating boards and hard boards of all types, and also as reinforcement and dimensional stabilizers for making a large number of laminate products and for a myriad of other uses. These mats are made on a conventional wet laid nonwoven mat machine except for a modification to the binder preparation system, an inventive step in the preparation of the binder and in the selection of ingredients for a binder slurry.
It is known to make nonwoven fibrous mats from fibers, such as glass, polyester, polypropylene, polyethylene, cellulose, ceramic and many other types of fibers, and to bond these fibers together into mats with a thermosetting or thermoplastic resin binder, like urea formaldehyde, acrylic, melamine formaldehyde with or without urea additions, polyvinyl acetate and other resins, or mixtures thereof to make fibrous nonwoven mats. Such mats are used to make a myriad of roofing, building and automotive products. It is also known to use an acrylic copolymer latex, such as a self-cross linking acrylic copolymer of an anionic emulsifying type as one component of at least a two component binder for bonding glass fibers and particulate thermoplastic to make a glass fiber reinforced sheet that can later be hot molded into various shapes and articles, as disclosed in U.S. Pat. No. 5,393,379. It is also known to face gypsum board with fibrous nonwoven mats as disclosed in U.S. Pat. Nos. 5,772,846 and 4,647,496.
It is also known to add particles of thermoplastic resin to an aqueous fiber slurry used to make a mat that can later be hot stamped or thermoformed. When this is done, the resulting nonwoven mat is uniform throughout its thickness. Examples of nonwoven fiber glass mat containing particles of thermoplastic like polyvinyl chloride, polypropylene, etc. are disclosed in published European Patent Applications 0148760 and 0148761. In EP 0148760 the mat is bound together with aqueous binders like polyvinyl alcohol, starch, phenol formaldehyde, etc. According to the disclosures of both these EP applications the particulate thermoplastic component(s) is present in the mat in amounts of 40-80 percent by weight, and the mat is subjected to elevated temperature and pressure to fuse and consolidate the thermoplastic particles into a continuous thermoplastic matrix reinforced with glass fibers. Such mats would not be suitable as a facing for the insulating gypsum board product, such as the board disclosed in U.S. Pat. No. 4,647,496.
One surface of fibrous nonwoven mats made on a wet laid mat machine having no coating equipment thereon usually differs slightly from the opposite surface due to binder migration and/or one side laying on a wire belt while the other side is fully exposed and not in physical contact with any confining article during forming and drying. Nevertheless, the two sides are fairly similar in permeability and smoothness and both sides have fibers exposed. It is known to coat a mat on-line after drying and to spray very light or very thin coating compositions on a wet mat before drying. These coating methods either require extra equipment and mat handling or are inadequate for heavier coatings unless the forming speed is slowed down to unacceptable levels or for coatings containing particles over certain sizes. It is also known to coat a nonwoven mat, usually in a secondary operation, to seal one surface of the mat and/or to produce a smoother surface.
It would be desirable to make a mat having a smooth and less permeable surface at normal mat forming speeds without having to add equipment to the machine above the formed mat where it gets dirty and is difficult to clean without getting foreign material into the mat being produced and without adding substantial additional processing operations to the nonwoven mat processes and lines. While gypsum board faced with fiber glass mats has performed well in the past, it is desirable to hide the glass fibers better to prevent the fibers at the surface of the mat from partly or entirely breaking loose and from presenting a rough surface; but this has not been accomplished to the degree desired prior to this invention.
The present invention includes a multiple layer fibrous nonwoven mat having a body portion, the body portion comprising a mass of nonwoven fibers, with or without particles, bonded together with a resin binder, and a surface portion containing fibers and/or particles bonded together with the same said resin binder, the surface portion being substantially different than the major or body portion of the nonwoven mat. The body portion makes up a major portion of the basis weight (weight per unit area) of the mat while the surface portion makes up a minor portion of the basis weight of the mat. The fibers used for the surface portion are preferably shorter than one-quarter inch and longer than 100 microns.
Particles, when used in the surface portion according to this invention, are preferably sized so that less than a few percent, preferably less than one wt. percent of the particles will pass through the openings between the fibers in the nonwoven mat. The smaller the diameter of the fibers in the body portion the smaller the openings in the body portion and the smaller the particles and fibers that can be used in the surface portion. Preferably, the particles are within the size range of minus 40 and plus 100 U.S. standard mesh and can be of a lower bulk density than water. If the particles are too small, too many will flow part way or all the way through the body portion of the mat which is less desirable. It is permissible for some or a small portion of particles to flow into at least an interface portion of the body portion of the mat. This latter embodiment produces a better bond between the two layers, the body portion and the surface portion, and also helps to raduce the permeability of the layered mats. The surface portion of the mat of the present invention has a substantially lower permeability or pore size, or both, than the body or major portion of the fibrous nonwoven mat. An exposed surface of the surface portion can also be substantially smoother than an exposed surface of the body portion of the fibrous nonwoven mat. Preferably, at least 99 percent of the particles or fibers in the binder put onto the mat end up in the surface portion layer of the multiple layer nonwoven mat. Preferably the multiple layer mats of the present invention have two layers, a body portion layer and a surface layer portion.
The invention also includes a method of making the fibrous nonwoven mat described above comprising dispersing fibers, such as glass fibers, in an aqueous slurry, collecting the dispersed fibers onto a moving permeable support to form a fibrous nonwoven layer, removing excess water from the fibrous nonwoven layer, applying an aqueous resin latex binder containing particles and/or fibers to the top surface of the rapidly moving wet nonwoven fibrous layer, removing excess latex or aqueous resin, drying the nonwoven mat and curing the resin binder to form a nonwoven mat having a surface layer that differs substantially from the fibrous nonwoven body of the mat. The aqueous resin binder can also be foamed before using.